I wouldn't worry all the much, Doublewide, going thorugh the Gulfstream is a pretty good testiment. T

http://svdoublewide.com/2014/01/17/reflections-on-a-gulf-crossing/

Mark,

I looked at yours and Michelle's nice website: http://www.svreach.com/ ...In particular some of your pictures on "Boat Blog" portion of your site.

It sure looks like the rudder stock you have is a larger diameter than 2"? It doesn't look "puny" in any way. On the post bottom-painting post, it almost looks like the space betwen the hull and the top of the rudder is much narrower -- but on the other shots, it looks like there is more space? Is there some collar that makes the tube look bigger?

To my eye, your rudder position is in a lot more efficient position to direct your boat under sail. The area and proportion of your rudders are much more like the deeper rudder picture on the monohull in your post. (Your boat has two hulls which look like sailboat hulls. Take back my comment on checking powerboat rudders for referenece!)

I'd check the stops on the rudders first. There have been a bunch of Manta 40's -- I didn't find any chatter on problems with the rudders.